Ziegler-Natta catalysts for propylene polymerization – Interaction of an external donor with the catalyst (original) (raw)
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Propylene polymerization using supported Ziegler-Natta catalyst systems with mixed donors
Journal of Applied Polymer Science, 2012
Magnesium dichloride supported titanium catalyst incorporated with varying concentration of ethylbenzoate and diisobutyl phthalate together as internal donor are synthesized. The synthesized catalysts are characterized and compared with respect to composition, phase characteristics, crystallite size, and particle morphology. Performance of catalysts containing mixed donors is compared with the conventional single donor-based catalysts. The polymerization studies of the catalysts for propylene polymerization show dependence of polymerization kinetics on relative concentration of diisobutyl phthalate and ethylbenzoate. Molecular weight characteristics of polypropylene obtained from these catalysts are studied and correlated with the nature and concentration of donors present in the catalyst. Morphology replication from catalyst precursor to polymer is observed irrespective of the nature of donor being incorporated in the synthesized catalyst.
A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods
Materials, 2017
Ziegler-Natta polymerization catalysts were characterized by a complex of surface-and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti 4+ , Ti 3+ , Ti 2+ , and Ti 1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom.
Journal of Polymer Science Part A: Polymer Chemistry, 2002
Hydrogen is a very effective chain transfer agent in propylene polymerization reactions with Ti-based Ziegler-Natta catalysts. However, measurements of the hydrogen concentration effect on the molecular weight of polypropylene prepared with a supported TiCl4/dibutyl phthalate/MgCl2 catalysts showed a peculiar effect: hydrogen efficiency in chain transfer significantly decreases with concentration and, at very high concentrations, hydrogen does not affect the molecular weight of polypropylene anymore. Detailed analysis of kinetic features of chain transfer reactions for different types of active centers in the catalyst suggests that chain transfer with hydrogen is not merely the hydrogenolysis reaction of the Ti-C bond in an active center but proceeds with the participation of a coordinated propylene molecule.
Chemistry & Chemical Technology, 2010
Different methods to remove the alcohol of adduct MgCl2nEtOH were studied to obtain Ziegler-Natta catalysts for evaluation in ethylene and propylene polymerization. Thus, the adduct MgCl2nEtOH was submitted to thermal dealcoholation, as well as chemical dealcoholation with different substances: titanium tetrachloride, triethylaluminum, and dichloro-dimethylsilane. Thermogravimetric analyses (TGA) were performed to obtain information on the thermal characteristics of adducts and prepared supported catalysts. Ethylene and propylene homopolymerization were carried out with the prepared catalysts and the polymers were characterized.
Macromolecular Chemistry and Physics, 2009
An insight on the influence of ethyl benzoate (EB) and diisobutyl phthalate (DIBP) as internal donors, differing in coordination nature on the structural aspects of MgCl 2 matrix in highperformance MgCl 2 -supported titanium catalysts was developed using FTIR spectroscopy and WAXD studies. The analysis of the >C --O stretching IR band of internal donors showed their coordination to and lateral cuts of MgCl 2 matrix. Transformation of magnesium ethoxide {Mg(OEt) 2 } to MgCl 2 during catalyst preparation resulted in different MgCl 2 phases, namely the a-form, b-form, and the disordered d-form, which were analyzed by WAXD studies. The results from WAXD showed the relative preference of a-form over b-form in case of DIBPbased catalysts, which might be due to interlayer bridging between adjacent layers due to the bidendate nature of DIBP. This can be one of the reasons for the high productivity of dialkylphthalate-based catalysts in comparison to ethyl-benzoate-based catalyst systems.
Journal of Applied Polymer Science, 1997
Anhydrous magnesium dichloride was reacted with silicon tetraethoxide to form a solid adduct. The adduct was treated with titanium tetrachloride and an internal Lewis base to prepare supported titanium catalysts. Alkyl benzoate (PhCOOR, R Å Me, Et, n 0 Bu) or dialkyl phthalate [Ph(COOR) 2 , R Å Me, Et, n 0 Bu] was used as an internal Lewis base. The prepared catalysts (MT) in combination with triethylaluminum as a cocatalyst polymerize propylene to yield polypropylene. The nature and concentration of internal Lewis base influence the composition, specific surface area, and performance of the catalysts. The addition of diphenyl dimethoxysilane into the MT/Et 3 Al catalyst system increases the isotactic index of polypropylene from 75 to 97 at a Si/Al mol ratio of 0.05. The overall results indicate that a dialkyl phthalate-incorporated catalyst shows better physical, chemical, and polymerization characteristics compared to a corresponding alkyl benzoate catalyst.
Polymer, 1996
Magnesium dichloride supported titanium catalysts were prepared by solubilizing anhydrous magnesium dichloride in 2-ethyl-l-hexanol followed by treatment with titanium tetrachloride. 2,2-Dimethoxypropane was used as an internal Lewis base. Solid products were characterized by compositional analysis, and specific surface area. Titanium magnesium catalysts (Ti Mg) in conjunction with triethylaluminium showed high activity (5110g PP/g Ti) and high stereospecificity (I.I = 92) for propylene polymerization. The variation in the amount of 2,2-dimethoxypropane during catalyst synthesis governs the productivity of the catalyst. Furthermore, the increase in the chain length of the alkyl group from ethyl to hexyl of trialkylaluminum cocatalyst retards the activity of the catalyst system, with minor variation in the isotactic index of polypropylene. The addition of diphenyldimethoxysilane into triethylaluminum further improves the stereospecificity of the catalyst system.
Designed Monomers and Polymers, 2006
The propagation mechanism of 1-alkenes, especially propylene, for newly developed catalysts such as metallocene catalysts and bis(phenoxy-amine)zirconium-based catalysts and traditional Ti-based Ziegler-Natta catalysts, and the relationship between the structure of the catalyst and the structure of polyolefins produced, was reviewed. We believe that the propagation mechanism of 1alkenes, especially propylene, for traditional Ti-based heterogeneous catalysts and the relationship between the structure of the catalyst and the structure of polyolefins produced is elucidated more explicitly with metallocene catalysts and bis(phenoxy-amine)zirconium-based catalysts as reference.